Field
Embodiments of the disclosure generally relate to the field of semiconductor manufacturing processes and devices, and more particularly, to methods for forming silicon-containing epitaxial layers for semiconductor devices.
Description of Related Art
Size reduction of metal-oxide-semiconductor field-effect transistors (MOSFETs) has enabled the continued improvement in speed performance, density, and cost per unit function of integrated circuits. One way to improve transistor performance is through application of stress to the transistor channel region. Stress distorts (i.e., strains) the semiconductor crystal lattice, and the distortion, in turn, affects the band alignment and charge transport properties of the semiconductor, By controlling the magnitude of stress in a finished device, manufacturers can increase carrier mobility allowing for faster device performance.
One approach of introducing stress into the transistor channel region is to incorporate a dopant into the region during formation of the region. The dopant can occupy a lattice site in a semiconductor crystal. The different size of the dopant atoms relative to the other repeating units, such as silicon atoms, in the crystal structure causes the strain that increases the carrier mobility. For example, phosphorous atoms can be used as dopants to strain a primarily silicon semiconductor crystal lattice.
A silicon layer doped with phosphorous atoms can be formed using an epitaxial process, such as a selective epitaxial process. A selective epitaxial process can include a deposition step and an etching step to produce a crystalline layer. Often, a goal of an epitaxial deposition and etch is to produce an epitaxial layer with high strain and low resistivity allowing for faster switching speeds and low power consumption in the devices using the epitaxial layer. Creating the epitaxial layer with high strain can be an expensive process due to the amount of dopant precursor needed as well as the time that for the dopant concentrations in the epitaxial layers to reach the specified level. Creating epitaxial layers with low resistivity can also be an expensive process because additional steps after etching are often required when etching undesirably raises the resistivity of the epitaxial layers.
Therefore, there is a need for a method and apparatus for reducing the costs of creating epitaxial layers with high strain and low resistivity.